1. Field of the Invention
The present invention relates to a tubular material for manufacturing a precision-tube drawing apparatus comprising a drawing bench for drawing a tubular material (round tube, angular tube, deformed or profile tube) and, more particularly, to an apparatus for manufacturing a drawn precision-tube which has high dimensional precisions (bending, twisting, roundness (in the case of a round tube), nonuniform section) and high surface precision.
2. Description of the Related Art
In a conventional drawing bench, a back bench having a plug set device for reciprocating a plug rod while a rear end of the plug rod is held at a drawing core, and carriage rails having a die stand with a die fixed at its rear end portion in a drawing direction are arranged in tandem. After a tube element is fitted on a plug and the plug rod, the front end of the tube element is guided to the die, and the plug is moved forward to be guided to the distal end of the tube element. Thereafter, the tube element is chucked and drawn by a car carriage traveling along the carriage rails.
In the conventional drawing bench described above, the tube element which is fitted on the plug and the plug rod is held by only the plug rod before drawing. For this reason, when the distal end of the tube element is set in the die, the plug rod receiving the weight of the tube element is flexed, and during drawing, the central line of the tube element cannot coincide with the drawing central line. During drawing, the rear end of the tube element is unstable and is vibrated more or less, thus degrading dimensional precisions, e.g., causing a nonuniform section or bending of a drawn tube.
Since the conventional carriage is of car type, it is easily vibrated during drawing travel, and this also causes a nonuniform section and bending of a product. With such a drawing bench, the surface of the drawn tube is easily scratched or indented.
Therefore, when the drawn tube is used for a precision part such as a photosensitive drum of a copying machine and a magnetic drum, bending of the drawn tube must be corrected by a roller, and its surface must be ground.